The invention uses a scintillation method of converting energy of radiating particles into a luminous flux which is subsequently converted into an electrical signal by photomultiplier tubes. A test substances is mixed with a scintillation solution whereby a "cocktail" is formed.
The aforesaid method involves refined recording techniques which are highly sensitive, a factor having particular importance in finding softly radiating low-intensity isotopes.
There is known a liquid scintillation counter comprising a detector with a measuring chamber and photomultiplier tubes which is surrounded by a protective shell and having a hole in the bottom portion of the measuring chamber. The known counter also includes a device for delivering a test specimen placed in a receiving assembly, said device being coupled to an electric motor, a vertical light shutter coupled to another electric motor, and a plate having a hole and suited to accommodate a plurality of test specimens and deliver them to the detector (cf. U.S. Pat. No. 3,270,202). The foregoing liquid scintillation counter is characterized by that the detector with the measuring chamber and photomultiplier tubes is disposed above the plate and the receiving assembly, the device for delivering test specimens is arranged below the plate, and the receiving assembly is found in the hole in said plate and made to enable upward movement of test specimens into the measuring chamber of the detector and back. The vertical light shutter is made as a hollow cylinder capable of moving in a vertical direction and encompassing the receiving assembly. The receiving assembly comprises a cylindrical head tapered in its upper portion which is secured at the top on the cylinder of the telescopic assembly of the device for delivering a test specimen.
The receiving assembly is initially found in the lower position at the plate level and receives a test specimen from a corresponding section of a conveyer, while the vertical shutter is found in the upper position inside the measuring chamber of the detector. In operation the vertical light shutter moves down. After it stops in a new position, the receiving assembly containing the test specimen moves up into the measuring chamber. The test specimen is returned from the measuring chamber in reverse order.
The counter under review has been generally unsatisfactory due to its considerable height conditioned firstly by position of the detector above the plate at a level higher than the flask containing the specimen and secondly by the height of the device for delivering a test specimen to the measuring chamber, which is located below the plate. Said plate isolates the device for delivering a test specimen from the measuring chamber of the detector, a limitation preventing effective protection of the measuring chamber against light.
Another disadvantage of the counter under review is that the device for delivering a test specimen and the light shutter are actuated by two motors, the sequence of their operations being controlled by an automatic control circuit in accordance with a predetermined program, a feature substantially complicating the entire device and decreasing its operational reliability. Moreover, said position of the detector prevents installation of a test specimen directly on the receiving assembly, a limitation making measurements of single specimens inconvenient.
The prototype of the present invention is a liquid scintillation counter (cf. U.S. Pat. No. 3,852,599, Cl. 250-328) comprising a detector with a measuring chamber and photomultiplier tubes, which is surrounded by a protective shell and has a hole in a bottom portion thereof, a plate having two holes and suited to accommodate a plurality of specimens, and a tube connecting one of the holes in the plate with a hole in the measuring chamber of the detector. The aforesaid counter also includes three delivery means with pneumatic actuators and receiving assemblies for transferring a test specimen from the surface of the plate through the hole therein into the measuring chamber of the detector which is installed above the plate and connected with one of its holes via a tube forming a light-proof channel.
The afore-mentioned counter is characterized by that the process of delivering a test specimen from the surface of the plate out of a respective section of the conveyor to the measuring chamber of the detector and back consists of three stages, each of which involves the use of different delivery means with associated receiving assemblies and pneumatic actuators, relative movement of each delivery means being controlled by a device enabling automatic control of movement of a test specimen through limit switches.
The receiving assembly of the first means initially receives a test specimen from a respective section of the conveyer, said first means being set to the upper position. The second means displacing a test specimen in a horizontal direction is prepared to receive the test specimen from the first means into its receiving assembly. The third means placed in the lower position is ready to receive the test specimen into its receiving assembly. In operation, the first receiving assembly moves the test specimen downwards to a position at which it enters the receiving assembly of the second means which moves the test specimen in a horizontal plane until it is placed in the receiving assembly of the third means. Said third means moves up vertically the test specimen through a respective channel into the measuring chamber of the detector. The test specimen is returned to the plate in the respective conveyer section in reverse order.
The receiving assemblies of vertical transmitters include cylindrical tables secured in the upper portion of rods which are linked with the pneumatic actuators.
The receiving assembly of the device accomplishing horizontal displacement comprises a piston having holes, a bottom portion thereof being provided with a circular lug adapted to accommodate a test specimen on completion of the first delivery stage. The piston coupled to the pneumatic actuator is installed in the hollow horizontal cylinder in a manner allowing its displacement inside said cylinder which has four holes adapted to pass a test specimen in a vertical direction. Also, the piston compised in said counter acts as a light shutter to protect the measuring chamber of the detector against light. For this purpose, its cylindrical portion accommodates two annular seals.
The known counter has been generally unsatisfactory due to its considerable height conditioned by the fact that the detector is arranged above the plate adapted to accommodate a plurality of test specimens at a level exceeding that of the flask containing a test specimen, the device accomplishing horizontal movement of a test specimen is located below said plate and the devices enabling vertical displacement thereof are disposed below the device accomplishing said horizontal movement and representing air cylinders whose height depends on the height to which the receiving assemblies are lifted.
Another disadvantage of the known counter is that the device enabling horizontal transfer of said flask has a considerable structural length determined by a horizontal stroke and dimensions of the pneumatic actuator, a factor substantially increasing its volume.
Also, as the movement of a test specimen from the plate out of a respective conveyer section to the measuring chamber of the detector involves three stages in transferring the flask containing a test specimen from one receiving assembly to another and therefrom to the third receiving assembly, each receiving assembly being provided with an individual transfer means with a pheumatic actuator, there arises the need for controlling the sequence of their operations by the use of an automatic control circuit in accordance with a predetermined program, a disadvantage complicating the entire device and decreasing operational reliability thereof.